Updated 10/31/2013 at 5:23 p.m. ET
(CNN) - Republicans blocked two high-profile presidential nominees on Thursday as the bitter fight over appointments escalated in the U.S. Senate, but Democrats held their fire and decided, for now, to forgo a change in rules to limit filibusters.
The GOP mounted filibusters against Judge Patricia Millett, who was appointed by President Barack Obama to the U.S. Appeals Court for the District of Columbia, and Rep. Melvin Watt, who was named to head the agency that oversees housing finance giants Fannie Mae and Freddie Mac.
Democrats fell short in procedural votes called to move forward on the nominations, testing their patience and raising serious questions about how they might respond.
Although it was raised as a possibility, Democrats are not expected at this time to invoke the so-called "nuclear option" to change filibuster rules, two Senate Democratic leadership aides told CNN.
Many rank-and-file Democrats wanted the change, over objections from minority Republicans, to allow the Senate to approve appointments with a simple majority vote rather than the 60 now needed to proceed with a nomination.
But Democratic leaders are reluctant to engage a knock down fight with Republicans at the same time they need to move other legislative priorities through the Senate.
Next week, the Senate will take up a key piece of gay rights legislation, and Democrats believe they are just one vote shy getting it passed and don't want to jeopardize their prospects by angering Republicans with a rule change effort.
The Senate also will soon enough turn its attention back to the fiscal issues in desperate need of bipartisan cooperation.
Opposition to appointments
Republicans argued that Millett's appointment to the judicial post that has been a stepping stone for some to the U.S. Supreme Court was unnecessary.
They said the appeals panel now is evenly divided between judges appointed by Republican and Democratic presidents and doesn't have enough work to justify an additional member even though there are three vacancies.
Democrats said the filibuster was a transparent attempt to maintain conservative influence on the court.
Earlier in the day, Republicans also blocked Obama's nomination of Watt, a North Carolina Democrat, to head the Federal Housing Finance Agency, an independent federal entity that has been in control of Fannie and Freddie since their taxpayer rescue last decade during the housing crisis.
Republicans argued Watt is not independent enough and lacks expertise to run the agency.
Fannie and Freddie own or guarantee more than half of all outstanding mortgages in the United States, according to the Congressional Budget Office.
Opening from Biden
The push to change the rules appeared to get a boost when Vice President Joe Biden, who served in the Senate for decades, said it was "worth considering."
The opening from Biden reflects the thinking of many Democrats who want to push for the controversial change.
For instance, Sen. Jeff Merkley, D-Oregon, was frustrated with the Millett vote, especially.
"This is declaring war on the judicial branch. This is declaring war on the executive branch. It is inconsistent with the traditions of the Senate," he said. "This type of blockade cannot stand."
Sen. Sherrod Brown, D-Ohio, complained the fight was "all about ideology" and said he thought support was "growing for changing the rules when they play these games."
But other veteran Senate Democrats who have seen the majority change hands between the parties over the years are opposed, saying they want to preserve the right to filibuster in the future.
"I've never favored using the nuclear option," said Sen. Carl Levin, D-Michigan, who chairs the Armed Services Committee and who is retiring from the Senate after this term.
The second-ranking Senate Republican warned that Democrats need to "think twice" about changing the rules.
Or, he said, the "next time there is a Republican president and Republicans hold a majority in the Senate then we could confirm another (Antonin) Scalia, another (Clarence) Thomas with 51 votes," Senator John Cornyn of Texas said, referring to the two conservative Supreme Court justices.
–CNN's Bill Mears contributed to this report.